Bipolar high-voltage network and method for operating a bipolar high-voltage network

ABSTRACT

An aircraft bipolar high-voltage network includes a DC voltage converter comprising two unipolar input connections, two bipolar output connections and a reference potential connection, and at least one unipolar device having two electrical connections which are each coupled to one of the two unipolar input connections. The DC voltage converter has a first DC voltage converter module coupled to a first of the unipolar input connections via a module input connection, to the reference potential connection via a module reference potential connection and to a first of the bipolar output connections via a module output connection, and a second DC voltage converter module coupled to a second of the unipolar input connections via a module input connection, to the reference potential connection via a module reference potential connection and to a second of the bipolar output connections via a module output connection.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the German patent application No.102014203157.5 filed on Feb. 21, 2014, the entire disclosures of whichare incorporated herein by way of reference.

FIELD OF THE INVENTION

The present invention relates to a bipolar high-voltage network and to amethod for operating a bipolar high-voltage network, in particular forthe distribution of electrical power in an aircraft or spacecraft.

BACKGROUND OF THE INVENTION

Bipolar high-voltage voltages, for example ±270 V bipolar DC voltage,are often required in aircraft. Generators and appropriate rectifiersare usually used to provide voltages of this type.

EP 2 624 433 A1 discloses two non-isolated DC voltage converter unitswhich are connected in parallel and have a neutral point, which isgalvanically isolated from a neutral point of the DC voltage converterunits, of an AC voltage filter connected downstream of the DC voltageconverter units for feeding DC voltage generated by photovoltaic cellsinto an AC voltage network.

US 2009/0085537 A1 discloses a non-isolated boost converter for DCvoltages, in which a unipolar input DC voltage is converted into abipolar output DC voltage by two coupled boost converter units.

The document “Analyse einer neuartigen elektrischen Konverterarchitekturzur Integration von Brennstoffzellen auf Gesamtsystemebene” [“Analysisof a new electrical converter architecture for the integration of fuelcells to the overall system plane”] by A. Lücken, H Lüdders, T. Kut, S.Dickmann, F. Thielecke and D. Schulz, Deutscher Luft- undRaumfahrtkongress 2012 [German Aeronautics and Astronautics Congress],Berlin, Deutsche Gesellschaft fur Luft- und Raumfahrt [German Societyfor Aeronautics and Astronautics]-Lilienthal-Oberth e.V., Bonn, 2012,discloses a fuel cell system having two fuel cell stacks which arearranged in a series-connected manner and supply positive and negativeoutput voltages for one DC voltage converter module in each case, inorder to generate positive and negative high-voltage DC voltages for abipolar DC voltage network in an aircraft.

The document “Symmetrical Boost Concept for Solar Applications up to1000V” by M. Frisch and T. Erno, Vinotech GmbH, 2009 discloses atransformer-less DC voltage converter for solar cells for generatingmulti-phase AC voltages.

SUMMARY OF THE INVENTION

There is, however, a need for solutions for high-voltage networks inaircraft that are reliable and highly available, yet still have a lowsystem weight and can be operated by connection devices of variousvoltage consumptions.

Therefore, according to a first aspect of the invention, there isprovided a bipolar high-voltage network for an aircraft or spacecraft,comprising a DC voltage converter which comprises two unipolar inputconnections, two bipolar output connections and a reference potentialconnection, and at least one unipolar device having two electricalconnections which are each coupled to one of the two unipolar inputconnections. The DC voltage converter comprises a first DC voltageconverter module which is coupled to a first of the unipolar inputconnections of the DC voltage converter via a module input connection,to the reference potential connection of the DC voltage converter via amodule reference potential connection and to a first of the bipolaroutput connections of the DC voltage converter via a module outputconnection, and comprises a second DC voltage converter module which iscoupled to a second of the unipolar input connections of the DC voltageconverter via a module input connection, to the reference potentialconnection of the DC voltage converter via a module reference potentialconnection and to a second of the bipolar output connections of the DCvoltage converter via a module output connection.

Furthermore, according to a second aspect of the invention, an aircraftor spacecraft having one or more bipolar high-voltage networks accordingto the invention is provided according to a first aspect.

According to a third aspect, the invention further provides a method foroperating a high-voltage network according to the invention, comprisingthe steps of operating the DC voltage converter in order to output abipolar voltage between the bipolar output connections and the referencepotential connection of the DC voltage converter, detecting whether ashort circuit is present between a first of the bipolar outputconnections and the reference potential connection and/or whether ahigh-resistance fault is present at a first of the bipolar outputconnections, and operating the DC voltage converter in order to output aunipolar voltage between the second of the bipolar output connectionsand the reference potential connection of the DC voltage converter if ashort circuit and/or a high-resistance fault has been detected. Themethod offers the advantage that in many fault situations, the bipolarhigh-voltage network is operated further in a mode of operation havingrestricted operating conditions (degraded mode of operation) in order toat least maintain a temporary emergency mode of operation.

In addition, using the method, the DC voltage converter is able to drivea short circuit current, at least up to the current load limit thereof.The process according to the method can make sub-networks of thehigh-voltage network open in the event of a short circuit, whichsub-networks are protected by fuses having overcurrent protection. Inthe event of a short circuit between a first of the bipolar outputconnections and the reference potential connection, the output voltageat said bipolar output connection drops and the output current risesabove a predetermined controller threshold. If the short circuit hasbeen caused by components in this sub-network, the sub-network can beisolated and the rest of the high-voltage network can then continue tobe operated as normal.

According to one embodiment of the high-voltage network according to theinvention, the DC voltage converter modules can each comprisenon-isolated DC voltage converters. Owing to the design as non-isolatedDC voltage converters, it is possible to advantageously reduce thesystem weight since heavy components such as transformers or additionalchokes can be omitted.

According to further embodiments of the high-voltage network accordingto the invention, the DC voltage converter modules can in this case eachcomprise down converters, up converters, inverse converters,cascade-connected down/up converters, cascade-connected two-pointdown/up converters, open-loop-controlled or non-open-loop-controlledtwo-point NPC converters or split-pi converters.

According to a further embodiment of the high-voltage network accordingto the invention, the high-voltage network can further comprise aunipolar up converter which is coupled between the unipolar inputconnections of the DC voltage converter and the module input connectionsof the DC voltage converter modules. In this case, the DC voltageconverter modules can each comprise down converters which in this casecan be formed in particular by an open-loop-controlled ornon-open-loop-controlled two-point NPC converter.

According to a further embodiment of the high-voltage network accordingto the invention, the high-voltage network can further comprise anopen-loop-controlled three-point NPC power converter, the input of whichis coupled to the two bipolar output connections and to the referencepotential connection of the DC voltage converter and the output of whichcomprises three AC voltage phase connections, and an LC filter stagewhich is coupled to the three AC voltage phase connections of theopen-loop-controlled three-point NPC power converter.

According to a further embodiment of the high-voltage network accordingto the invention, the high-voltage network can further comprise a firstDC voltage intermediate circuit, which is coupled between the unipolarinput connections of the DC voltage converter, and a second DC voltageintermediate circuit, which is coupled between the bipolar outputconnections of the DC voltage converter.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail in the following inconjunction with and in relation to the embodiments as in theaccompanying drawings.

The accompanying drawings give a better understanding of the presentinvention and show example variants of the invention. They serve toexplain principles, advantages, technical effects and possiblevariations. Naturally, other embodiments and many of the intendedadvantages of the invention are also conceivable, in particular in viewof the detailed description of the invention set out in the following.The elements in the drawings are not necessarily shown to scale, and areshown in a simplified form or schematically in some cases for reasons ofclarity. Like reference signs denote like or similar components orelements.

FIG. 1 is a schematic view of a bipolar high-voltage network accordingto an embodiment of the invention.

FIG. 2 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 3 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 4 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 5 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 6 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 7 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 8 is a schematic view of a DC voltage converter module for ahigh-voltage network according to FIG. 1 in accordance with a furtherembodiment of the invention.

FIG. 9 is a schematic view of a bipolar high-voltage network inaccordance with a further embodiment of the invention.

FIG. 10 is a schematic view of a bipolar high-voltage network inaccordance with a further embodiment of the invention.

FIG. 11 is a schematic view of a bipolar high-voltage network inaccordance with a further embodiment of the invention.

FIG. 12 is a schematic view of a method for operating a bipolarhigh-voltage network in accordance with a further embodiment of theinvention.

FIG. 13 is a schematic view of an aircraft having a bipolar high-voltagenetwork in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Although specific embodiments are described and shown herein, it isclear to a person skilled in the art that a wealth of additional,alternative and/or equivalent implementations can be selected for theembodiments, without substantially deviating from the basic idea of thepresent invention. In general, any variations on, modifications to andalterations to the embodiments disclosed herein should also beconsidered to be covered by the invention.

Any loads, power consumers, electrical energy stores, energy sources orsub-networks which can output and/or consume electrical DC voltagebetween two connections constitute unipolar devices in the context ofthe present invention. In particular, unipolar devices in the context ofthe invention can include fuel cells, photovoltaic cells, capacitors,accumulators, DC machines and other electrical loads or energy sources.

Any loads, power consumers, electrical energy stores, energy sources orsub-networks that have three electrical connections and can outputand/or consume two different electrical DC voltages, in particular DCvoltages of opposite polarity, between two of the connections in eachcase constitute bipolar devices in the context of the invention.Corresponding electrical networks that are operated with bipolar highvoltage, i.e., can consume and/or output bipolar voltage, thusconstitute bipolar high-voltage networks in the context of the presentinvention.

Electrical machines in the context of the present invention can include,for example, induction machines such as synchronous or asynchronousmachines, reluctance machines, split-pole machines, DC machines,repulsion machines or other types of machine.

FIG. 1 is a schematic view of a bipolar high-voltage network 10. Thebipolar high-voltage network 10 comprises a DC voltage converter 1 whichis fed a unipolar input voltage at two input connections 1 a and 1 b andconverts said unipolar input voltage into a bipolar output voltage atthe three output connections 2 a, 2 b and 2 c. The output connections 2a and 2 c are both DC voltage output connections 2 a and 2 c which areeach coupled to tapping terminals 4 a and 4 c. The output connection 2 bis a reference potential connection 2 b which is coupled to an earthpotential or reference potential 3 and can be tapped at a referencepotential terminal 4 b. Here, the terminals 4 a, 4 b and 4 c can becoupled to a bipolar network (not shown explicitly), for example to abipolar high-voltage network of an aircraft or spacecraft. When thebipolar high-voltage network 10 is used in an aircraft, a high-voltageDC voltage, for example ±270 V, which is bipolar with respect to thereference potential connection 2 b, can be tapped at the tappingterminals 4 a and 4 c. The reference potential 3 of the referencepotential connection 2 b can be fixed by appropriate actuation of the DCvoltage converter 1 and does not necessarily have to be located in thecenter between the two potentials at the output connections 2 a and 2 c.For example, an asymmetric bipolar high-voltage voltage can also beprovided at the tapping terminals 4 a and 4 c with respect to thereference potential connection 2 b, i.e., the sizes of the two bipolarvoltage portions generated by the bipolar high-voltage network 10 can bedifferent.

In this case, the DC voltage converter 1 comprises two DC voltageconverter modules 5 which are actuated separately. The DC voltageconverter modules 5 are each coupled to one of the unipolar inputconnections 1 a and 1 b via a module input connection 5 a, to thereference potential connection 2 b via a module reference potentialconnection 6 and to one of the bipolar output connections 2 a or 2 c ofthe DC voltage converter 1 via a module output connection 5 b. If theelectrical connections of one (or more) unipolar devices 8 are coupledto one of the two unipolar input connections 1 a or 1 b, the DC voltageconverter modules 5 can each generate, from the single input potential,a branch of the bipolar voltage supply to the module output connections5 b with respect to the reference potential 3 at the module referencepotential connection 6.

In this respect, the unipolar device 8 can comprise purely DC voltagesources, such as fuel cells, purely DC voltage loads, such as technicalloads of an aircraft, bidirectionally operable DC voltage devices, suchas motors/generators, or electrically rechargeable energy storagedevices, such as batteries or supercaps.

Depending on the type of the unipolar device 8, the DC voltage converter1 can in this case also be operated bidirectionally, i.e., the outputconnections 2 a and 2 c can also function as input connections forconverting a bipolar input voltage into a unipolar output voltage at theinput connections 1 a and 1 b acting as unipolar output connections.

The first (upper) DC voltage converter module 5 can be configured toprovide a first high-voltage DC voltage between the module outputconnection 5 b and the module reference potential connection 6.Similarly, the second (lower) DC voltage converter module 5 can bedesigned to provide a second high-voltage DC voltage between theassociated module output connection 5 b and the module referencepotential connection 6. Here, the first and second high-voltage DCvoltages can have a different polarity sign from the reference potential3, and can in particular be of the same value, for example +/−270 V or+/−135 V. It is of course also possible to actuate the two DC voltageconverter modules 5 in order to output high-voltage DC voltages ofdifferent sizes.

Due to the configuration in FIG. 1, an implicit redundancy of thehigh-voltage network 10 is ensured with respect to high impedances(“open circuit state”) at one of the output connections 2 a or 2 c orwith respect to short circuits between earth and one of the outputconnections 2 a or 2 c. This advantageously allows the high-voltagenetwork 10 to be operated in a restricted mode of operation (“degradedoperation”), so that only limited additional safety measures would haveto be taken. In particular, measures in the backend of the high-voltagenetwork 10 can be avoided, for example conditional switching elements ordiodes, with a corresponding simplification in implementation and areduction of costs. In the case of load operation of the DC voltageconverter modules 5, the connected loads and energy sources must thennaturally be operable at half the operating voltage, i.e., at anoperating voltage which is half the operating voltage in normaloperation.

Input-side and output-side intermediate circuits having intermediatecircuit capacitors 7 a and 7 b are used in each case to buffer voltagepeaks and to reject common-mode fluctuations.

FIGS. 2 to 8 schematically show, by way of example, variants of DCvoltage converter modules 5 of this type. In this context, the DCvoltage converter modules 5 in FIGS. 2 to 8 can be used in a DC voltageconverter, such as the DC voltage converter 1 in FIG. 1. Advantageously,two similar converter topologies can be implemented in parallel with oneanother in each case. The converter topologies all share the featurethat they each comprise non-isolated DC voltage converters. Non-isolatedDC voltage converters have a low system weight, since complex and heavytransformers can largely be omitted.

In FIG. 3, the DC voltage converter modules 5 are formed asbi-directional down converters 20 having charging capacitors 11 and 12,converter switches 13 and 14 and a choke 15. In FIG. 4, the DC voltageconverter modules 5 are formed as bi-directional up converters 30 havingcharging capacitors 11 and 12, converter switches 16 and 17 and a choke15. These types of converters are particularly advantageous forapplications with high power requirements, in which the ratio betweeninput and output voltage is close to 1.

As shown in FIG. 5, the DC voltage converter modules 5 can beimplemented as bi-directional inverse converters 40 having chargingcapacitors 11 and 12, converter switches 13 and 16, and a choke 15. Thistopology can guarantee both boost converter operation and step-downconverter operation in both converter directions, and offers the lowestnumber of active elements.

FIG. 6 shows DC voltage converter modules 5 each formed ascascade-connected down/up converters 50 having charging capacitors 11and 12, converter switches 13, 14, 16 and 17 and a choke 15.Cascade-connected down/up converters 50 can function in an efficientmanner in terms of power if the ratio between input and output voltageis close to 1.

FIG. 7 shows the DC voltage converter modules 5 each formed ascascade-connected two-point down/up converters 60 which comprisecharging capacitors 11 and 12, converter switches 13, 13 a, 14, 14 a,16, 16 a, 17 and 17 a and a choke 15. What are referred to as flyingcapacitors 18 a and 18 b are wired between half bridges, which are eachformed of two converter switches. A bridge voltage is applied to suchcascade-connected two-point down/up converters 60, which are often alsoreferred to as flying capacitor multilevel converters/inverters (FMCI),at the outer connections thereof to the half bridges, such that thecentral connection is used for tapping the output voltage. In this case,the flying capacitors have a potential which constantly shifts withrespect to an input connection of the half bridges.

According to FIG. 7, the DC voltage converter modules 5 can each includeopen-loop-controlled or non-open-loop-controlled two-point NPCconverters 70. For this purpose, zero diodes 19 (“neutral point clampeddiodes,” NPC diodes) can be wired in each case in the center tap betweenmultistage bridge branches formed of converter switches 14 a, 14 b, 14c, 14 d or 17 a, 17 b, 17 c and 17 d. In this respect, it can also bepossible to replace the zero diodes 19 with active switching elements,such as power semiconductor switches, or to wire active switchingelements in parallel with the zero diodes 19, so that it is possible toachieve an ANPC (active neutral point clamped) power converter. By meansof an appropriate switching strategy of the active switching elements,such as IGBT or MOSFET power semiconductor switches, the output voltagecan thereby be clamped in an active manner with respect to the referencepotential of the rectifier circuit. Series-connected charging capacitors11 and 11 a or 12 and 12 a are used to stabilize the voltage in themultiple voltage stages generated in each case. By using two-point NPCconverters 70, the power efficiency increases at the expense of thecircuit complexity.

As shown in FIG. 8, the DC voltage converter modules 5 can each comprisesplit-pi converters 80, which are formed of charging capacitors 11, 12,converter switches 13, 14, 16 and 17 and two chokes 15 a, 15 b. Thesplit-pi converter 80 is a series connection of two synchronousconverters which are buffered by an intermediate circuit capacitor 18 dtherebetween. In addition to the intermediate circuit capacitor 18 d, anintermediate circuit capacitor 18 c is provided, which couples a centraltap of the live bus rail between the synchronous converters of one ofthe split-pi converters 80 with the respective bus rail of the othersplit-pi converter 80′ of a DC voltage converter module 5. The split-piconverter 80 allows for both step-down converter operation and boostconverter operation in both energy flow directions. Owing to thecontinuous energy flow, the split-pi converter 80 is particularlyefficient and offers good electromagnetic compatibility (EMC).

By using two DC voltage converter modules 5 that can be operated andcontrolled, in a closed-loop manner, independently of one another,in-phase voltage fluctuations between the output connections 2 a or 2 cand the reference potential connection 2 b can be prevented, inparticular if the DC voltage converter modules 5 are operated incurrent-controlled closed-loop operation. This applies to all theconverter topologies 20, 30, 40, 50, 60, 70 and 80 in FIGS. 2 to 8.

The bipolar high-voltage network 10 in FIG. 9 is designed in a similarmanner to the split-pi converter 80 in FIG. 8. Instead of two bipolarboost converter stages at the module input connections 5 a, a unipolarup converter 90 can be used which overlaps the module, has a choke 15and converter switches 16 and 17, and is coupled between the unipolarinput connections 1 a, 1 b of the DC voltage converter 1 and the moduleinput connections 5 a of the DC voltage converter modules 5. The DCvoltage converter modules 5 then only have to each comprise downconverters, for example the down converter 20 as shown in FIG. 2. Theunipolar up converter 90 can be isolated from the DC voltage convertermodules 5 via an intermediate circuit capacitor 11. One requirement foran input-side unipolar up converter stage 90 is a closed-loop-controlledunipolar input voltage at the input connections 1 a and 1 b.

As shown in FIG. 10, a bipolar high-voltage network 10 can also beachieved, which implements down converters for the DC voltage convertermodules 5 in the form of half bridges of an open-loop-controlled ornon-open-loop-controlled two-point NPC converter 100. A two-point NPCconverter 100 allows the polarity of a unipolar input voltage to becommutated with respect to the output connections 2 a or 2 c via theinput connections 1 a and 1 b. In particular, when using DC voltagesources having a DC voltage that alternates in polarity, such as brushmotors in H-bridge operation, the two-point NPC converter 100 can takeover the necessary commutation. Bipolar LC stages formed in each case ofa choke 15 a or 15 b and a capacitor 11 a or 11 b can be used to filterthe unipolar input voltage.

In order to connect a bipolar high-voltage network 10 to an AC voltagenetwork, the high-voltage network 10 can comprise anopen-loop-controlled three-point NPC power converter 9 a, the input ofwhich is coupled to the two bipolar output connections 2 a, 2 c and tothe reference potential connection 2 b. The three-point NPC powerconverter 9 a comprises, at the output thereof, three AC voltage phaseconnections P1, P2 and P3, which are coupled via an LC filter stage 9 bto phase terminals A, B and C and to a neutral wire N of an AC voltagenetwork. Both closed-loop-controlled and non-closed-loop-controlled ACvoltage loads can be operated by means of the three-point NPC powerconverter 9 a, as shown in detail for example in Barbosa, P.; Steimer,P.; Steinke, J.; Meysenc, L.; Winkelnkemper, M.; Celanovic, N., “ActiveNeutral-Point-Clamped Multilevel Converters,” Power ElectronicsSpecialists Conference, 2005 (PESC '05), IEEE 36th, pp. 2296-2301, June2005.

The converter switches shown in FIGS. 2 to 11 can in each case bedesigned as power semiconductor switches, for example MOSFET switches,IGBT switches, BJT switches, JFET switches, bipolar transistors orsimilar switching elements.

FIG. 12 is a schematic view of a method M for operating a bipolarhigh-voltage network, in particular the high-voltage network 10 shownand described in connection with FIGS. 1 to 11. The method M can beused, for example, if one of the bipolar output connections 2 a or 2 cof the DC voltage converter 1 fails, for example if there is anexcessively high impedance of one of the output connections 2 a and 2 c,i.e., in the event of a high-resistance earth fault, or if there is ashort circuit between one of the output connections 2 a and 2 c and thereference potential connection 2 b.

As the first step S1, the method M comprises operating the DC voltageconverter 1 to output a bipolar voltage between the bipolar outputconnections 2 a or 2 c and the reference potential connection 2 b of theDC voltage converter 1. This is the normal mode of operation of the DCvoltage converter 1 for achieving a bipolar voltage supply, for examplefor a bipolar high-voltage network in an aircraft or spacecraft. In stepS2, it is detected whether there is a short circuit between a first ofthe bipolar output connections 2 a and 2 c and the reference potentialconnection 2 b and/or a high-resistance fault at a first of the bipolaroutput connections 2 a or 2 c. If a fault of this type is present, aswitch can be made from the normal mode of operation into an emergencymode of operation by actuating, in step S3, the DC voltage converter 1to output a unipolar voltage between the second of the bipolar outputconnections 2 a and 2 c, i.e., the output connection not affected by thefault, and the reference potential connection 2 b of the DC voltageconverter 1.

In this case, the DC voltage converter 1 can also temporarily beoperated with a short circuit current if a short circuit has beendetected. In this connection, this can temporarily include a time periodwhich drives the DC voltage converter up to its current load limit. Ashort circuit is thus triggered in sub-networks of the high-voltagenetwork 10 that are protected by fuses having overload protection, sothat the corresponding overload protection of the sub-networks isactivated. If the short circuit has been caused by components in thesub-networks which have been disabled or deactivated as a result, therespective sub-network can be isolated by operating the DC voltageconverter 1 in the temporary short circuit current mode and the rest ofthe high-voltage network 10 can then continue to be operated as normal.

Operating the DC voltage converter 1 in the unipolar mode, i.e., in theemergency mode of operation, can temporarily guarantee a limitedoperational readiness, even if there were a fault in the system. Thisadvantageously increases the availability and reliability of thehigh-voltage network. In particular with the topologies for DC voltageconverter 1 or high-voltage networks 10 as shown in FIGS. 1 to 11, it ispossible to implement a unipolar emergency mode of operation of thistype in a simple manner by deactivating the DC voltage converter module5 that has been affected in each case and by using the other forgenerating the unipolar voltage.

FIG. 13 is a schematic view of an aircraft F comprising a bipolarhigh-voltage network, for example a bipolar high-voltage network 10according to FIGS. 1 to 11. The high-voltage network 10 can be used toachieve, in the aircraft, a bipolar DC voltage supply, for example ±270V, for DC voltage loads in the aircraft F.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

1. A bipolar high-voltage network for an aircraft or spacecraft,comprising: a DC voltage converter comprising two unipolar inputconnections, two bipolar output connections and a reference potentialconnection; and at least one unipolar device having two electricalconnections, each coupled to one of the two unipolar input connections,the DC voltage converter comprising a first DC voltage converter modulecoupled to a first of the unipolar input connections of the DC voltageconverter via a module input connection, to the reference potentialconnection of the DC voltage converter via a module reference potentialconnection, and to a first of the bipolar output connections of the DCvoltage converter via a module output connection, and the DC voltageconverter comprising a second DC voltage converter module coupled to asecond of the unipolar input connections of the DC voltage converter viaa module input connection, to the reference potential connection of theDC voltage converter via a module reference potential connection, and toa second of the bipolar output connections of the DC voltage convertervia a module output connection.
 2. The bipolar high-voltage networkaccording to claim 1, wherein the DC voltage converter modules eachcomprise non-isolated DC voltage converters.
 3. The bipolar high-voltagenetwork according to claim 2, wherein the DC voltage converter moduleseach comprise down converters.
 4. The bipolar high-voltage networkaccording to claim 2, wherein the DC voltage converter modules eachcomprise up converters.
 5. The bipolar high-voltage network according toclaim 2, wherein the DC voltage converter modules each comprise inverseconverters.
 6. The bipolar high-voltage network according to claim 2,wherein the DC voltage converter modules each comprise cascade-connecteddown/up converters.
 7. The bipolar high-voltage network according toclaim 6, wherein the DC voltage converter modules each comprisecascade-connected two-point down/up converters.
 8. The bipolarhigh-voltage network according to claim 2, wherein the DC voltageconverter modules each comprise open-loop-controlled ornon-open-loop-controlled two-point NPC converters.
 9. The bipolarhigh-voltage network according to claim 2, wherein the DC voltageconverter modules each comprise split-pi converters.
 10. The bipolarhigh-voltage network according to claim 2, further comprising: aunipolar up converter which is coupled between the unipolar inputconnections of the DC voltage converter and the module input connectionsof the DC voltage converter modules, wherein the DC voltage convertermodules each comprise down converters.
 11. The bipolar high-voltagenetwork according to claim 10, wherein the down converters of the DCvoltage converter modules are formed by an open-loop-controlled ornon-open-loop-controlled two-point NPC converter.
 12. The bipolarhigh-voltage network according to claim 1, further comprising: anopen-loop-controlled three-point NPC power converter, the input of whichis coupled to the two bipolar output connections and to the referencepotential connection of the DC voltage converter and the output of whichcomprises three AC voltage phase connections; and an LC filter stagewhich is coupled to the three AC voltage phase connections of theopen-loop-controlled three-point NPC power converter.
 13. The bipolarhigh-voltage network according to claim 1, further comprising: a firstDC voltage intermediate circuit which is coupled between the unipolarinput connections of the DC voltage converter; and a second DC voltageintermediate circuit which is coupled between the bipolar outputconnections of the DC voltage converter.
 14. An aircraft or spacecraftcomprising a bipolar high-voltage network, the bipolar high-voltagenetwork comprising: a DC voltage converter comprising two unipolar inputconnections, two bipolar output connections and a reference potentialconnection; and at least one unipolar device having two electricalconnections, each coupled to one of the two unipolar input connections,wherein the DC voltage converter comprises a first DC voltage convertermodule which is coupled to a first of the unipolar input connections ofthe DC voltage converter via a module input connection, to the referencepotential connection of the DC voltage converter via a module referencepotential connection, and to a first of the bipolar output connectionsof the DC voltage converter via a module output connection, and the DCvoltage converter comprising a second DC voltage converter modulecoupled to a second of the unipolar input connections of the DC voltageconverter via a module input connection, to the reference potentialconnection of the DC voltage converter via a module reference potentialconnection, and to a second of the bipolar output connections of the DCvoltage converter via a module output connection.
 15. A method foroperating the bipolar high-voltage network according to claim 1,comprising the steps of: operating the DC voltage converter in order tooutput a bipolar voltage between the bipolar output connections and thereference potential connection of the DC voltage converter; detectingwhether a short circuit is present between a first of the bipolar outputconnections and the reference potential connection and/or whether ahigh-resistance fault is present at a first of the bipolar outputconnections, and operating the DC voltage converter in order to output aunipolar voltage between the second of the bipolar output connectionsand the reference potential connection of the DC voltage converter if ashort circuit and/or a high-resistance fault has been detected.
 16. Themethod according to claim 15, wherein operating the DC voltage convertercomprises temporarily operating the DC voltage converter with a shortcircuit current if a short circuit has been detected.